The present invention relates to an apparatus for reproducing compressed audio video data recorded on an optical disc such as a CD-ROM, a DVD etc. a DAT or other recording media by motion compensation prediction and, in particular, relates to an apparatus for reproducing a still picture from a recording medium.
MPEG (Moving Picture Experts Group), which is the international standard of the compression/expansion of color motion pictures, has been rapidly spread and applied to computers, communications, broadcastings, entertainment etc. Of MPEG, MPEG1 (MPEG Phase 1) is employed in storage media such as a CD-ROM, a DAT etc. and MPEG2 (MPEG Phase 2) is employed in storage media such as a DVD etc., digital broadcasting, communications etc.
The data arrangement structure (bit stream) of MPEG is formed in a hierarchy structure as shown in FIG. 3. The sequence layer representing the entirety of one video program is constituted by a plurality of GOPs (Group of Picture) 1 each is information block formed on a unit basis of a predetermined number of flames. The GOP layer is constituted by plural pictures 2. The picture layer is constituted by plural slices 3 which are blocks formed by dividing the picture 2. The slice layer is constituted by a plurality of macro blocks (hereinafter called as MBs) 4. The MB layer is constituted by blocks 5 each formed by 8xc3x978 pixels (or scanning lines).
The one block 5 of 8xc3x978 pixels is a minimum unit for coding of MPEG, that is, DCT (Discrete Cosine Transform) processing. The MB 4 is constituted by six blocks in total, that is, four blocks 5 of luminance signal Y and two blocks 5 of color signals CB, CR. The MB 4 is the minimum unit for the motion compensation prediction. The motion vector for the motion compensation prediction is performed on a MB unit basis.
Further, GOP1 includes an intra coded picture (intra coded picture; hereinafter called as an I picture) which is video information being subjected to the intra-frame coding, an predictive coded picture (predictive coded picture; hereinafter called as a P picture) which is video information being subjected to a prediction coding for data in the past-direction, and a bidirectionally predictive coded picture (bidirectionally predictive coded picture; hereinafter called as a B picture) which is video information being subjected to a timely bidirectional prediction coding. As shown in FIG. 4, one GOP 1 is constituted by predetermined numbers of I, P and B pictures which are set in advance.
In the reproduction mode, the respective I, P and B pictures shown in FIG. 4 are sequentially reproduced. In the still picture mode, one of the I, P and B pictures is reproduced as a still picture. In this case, since the prediction methods of the respective I, P and B pictures quite differ from one another as described above, the compression rates of image of these pictures also differ from one another. In the still picture mode, when a picture stops at the picture B having the highest compression rate, the picture quality of this picture is quite degraded as compared with the picture quality of the other I and P pictures when the picture stops at these pictures.
However, in the conventional still picture mode, the picture in a still state is reproduced as a still picture as it is. Thus, there is a problem that when a picture stops at the picture B, the reproduced display image of this picture is quite poor.
Further, since the number of the B pictures is quite larger than those of the I pictures and the P pictures, the probability in the still picture mode that a picture stops at the B picture is higher than the probability that a picture stops at the I picture or the P picture. As a result, the picture quality in the conventional still picture mode is not so good in general.
Such a reproducing method of compressed audio video data of MPEG system is disclosed in Japanese Patent Publications Nos. 10-32821A and 10-271445A, for example. In the former publication, when the MPEG coding image data has data processing information relating to the decoding image data, the decoding image data is monitored on a one-picture frame unit basis of the MPEG coding. The MPEG coding image data relating to the picture frame where the data processing information exists is transmitted on a packet unit basis of the data processing information. Thus, the former publication does not relate to the still picture reproduction.
On the other hand, in the latter publication, when displaying a still picture by the interlace system, a still picture on a frame unit basis and a still picture on a field unit basis are outputted in accordance with the contents of an image recorded on a recording medium, whereby a still picture having no blur and being legible can be provided. Thus, the of the latter publication requires two pictures.
Accordingly, an object of the present invention is to provide a still picture with good picture quality by simple processing.
In order to achieve the above object, there is provided an apparatus for reproducing a still picture from compressed video audio information including intra coded pictures, predictive coded pictures and bidirectionally predictive coded pictures recorded on a recording medium by selecting one picture from the compressed video audio information by means of a motion compensation prediction, comprising:
a selecting section for, when the reproduction is paused at one bidirectionally predictive coded picture, selecting either one intra coded picture or one predictive coded picture which is closest to the paused bidirectionally predictive coded picture; and
a display section for displaying either one intra coded picture or one predictive coded picture selected by the selecting section in place of the paused bidirectionally predictive coded picture.
According to such a configuration, when a picture stops at the bidirectionally predictive coded picture in a still picture mode, the intra coded picture or the predictive coded picture closest to the bidirectionally predictive coded picture is selected, and the intra coded picture or the predictive coded picture thus selected is displayed in place of the bidirectionally predictive coded picture.
Thus, since the intra coded picture or the predictive coded picture having better picture quality is displayed in place of displaying the bidirectionally predictive coded picture which is high in compression rate and not good in picture quality, it is possible to provide a still picture with good picture quality.
Preferably, the selecting section obtains a data difference between the paused bidirectionally predictive coded picture and the intra coded picture closest thereto, and a data difference between the paused bidirectionally predictive coded picture and the predictive coded picture closest thereto. And the selecting section selects one of the intra coded picture and the predictive coded picture having smaller data difference with respect to the paused bidirectionally predictive coded picture.
According to such a configuration, in the case of displaying the intra coded picture or the predictive coded picture in place of displaying the bidirectionally predictive coded picture, since the intra coded picture or the predictive coded picture having a smaller data difference from the bidirectionally predictive coded picture is displayed, a picture having less motion and good picture quality can be displayed as a still picture.
Preferably, the display section displays one of the intra coded picture and the predictive coded picture when the data difference obtained by the selecting section is not larger than a predetermined value. The display section displays the paused bidirectionally predictive coded picture when the data difference is larger than the predetermined value.
When the data difference of the intra coded picture or the predictive coded picture from the bidirectionally predictive coded picture is larger than the allowable value, even if the intra coded picture or the predictive coded picture is displayed in place of the bidirectionally predictive coded picture, it becomes quite difficult to recognize the relation with the bidirectionally predictive coded picture since the motion from the original bidirectionally predictive coded picture is quite large.
According to the above configuration, when the data difference is larger than the allowable value, since the original bidirectionally predictive coded picture is displayed, such a problem caused by displaying the intra coded picture or the predictive coded picture in place of the bidirectionally predictive coded picture can be eliminated that it becomes difficult to recognize the relation with the original bidirectionally predictive coded picture.
Preferably, the reproduction apparatus further comprises an operating section for setting a high quality display mode. The selecting section and the display section is operated only when the high quality display mode is set by the operating section.
According to such a configuration, a still picture with good quality can be displayed by setting the high picture quality display by operating the operation portion only when a user desires.
Preferably, the recording medium is a DVD. In this case, since it is possible to search a picture while looking a still picture with better picture quality at the time of retrieving image recorded on a DVD, a picture can be retrieved quite easily.
According to the present invention, there is also provided a method for reproducing a still picture from compressed video audio information including intra coded pictures, predictive coded pictures and bidirectionally predictive coded pictures recorded on a recording medium by selecting one picture from the compressed video audio information by means of a motion compensation prediction, comprising the steps of:
pausing the reproduction;
determining whether the reproduction has been paused at one bidirectionally predictive coded picture;
selecting either one intra coded picture or one predictive coded picture which is closest to the paused bidirectionally predictive coded picture when the reproduction has been paused at one bidirectionally predictive coded picture; and
displaying either one intra coded picture or one predictive coded picture selected by the selecting section in place of the paused bidirectionally predictive coded picture.
Preferably, the reproduction method further comprising the steps of:
obtaining a data difference between the paused bidirectionally predictive coded picture and the intra coded picture closest thereto, and a data difference between the paused bidirectionally predictive coded picture and the predictive coded picture closest thereto; and
selecting one of the intra coded picture and the predictive coded picture having smaller data difference with respect to the paused bidirectionally predictive coded picture.
Preferably, the reproduction method, further comprising the steps of:
determining whether the obtained data difference is larger than a predetermined value;
displaying the paused bidirectionally predictive coded picture when the data difference is larger than the predetermined value; and
displaying one of the intra coded picture and the predictive coded picture in place of the paused bidirectionally predictive coded picture when the data difference is not larger than the predetermined value.
Preferably, the reproduction method, further comprising the step of setting a high quality display mode. The selecting step and the display step is executed only when the high quality display mode is set.
Preferably, the recording medium is a DVD.